Numerous types of recordable media are available for storing digital data. One type of media available is recordable compact disk, known as a Compact Disk Recordable (CD-R). CD-R is a write-once optical medium containing an organic die layer fabricated over a layer of gold. The organic die layer is used for storing data and the gold layer is used to reflect light during a read operation. To store data on the CD-R medium, a recorder device is used to change the state of the organic die layer. Typically, a laser is provided in the recorder and used to change the state of the organic die in such a manner that the flection of a light source is modified. That is, during a read operation a focused light beam is directed through the organic die layer. If the light is reflected back to the light source, data stored at that location is in a particular state, for example a logical zero. If the light source is deflected, the data stored at that location is in a different state, for example a logical one.
A CD-R is structured into one or more tracks where a track represents an organized unit of information. The term `track` as used herein represents a continuous stream of information and is not to be confused with the concentric `tracks` found in random access recording media.
There are two different methods of writing data to a compact disk: packet writing, and track-at-once. Packet writing allows data to be written in small segments called `packets.` While packet writing is inherently safe and can be performed directly from a CPU application, it requires the CD recorder to be recalibrated to a home position prior to recording each packet. The required recalibration slows the recording process, and is thus is not suitable for high speed data replication systems.
The second method for data storage is track-at-once, or disk-at-once, and requires that a continuous uninterrupted stream of data be written to the medium at one time. If the data flow is interrupted, the medium is rendered useless. This is a result of the inability to locate the position of the last written data. An interruption of the data storage is referred to herein as an under-run.
Recordable media, such as CD-R are typically used in conjunction with a central processing unit (CPU) and a recording device. The recording device is used to store and retrieve data from the recordable medium in response to the CPU. The storage operation is typically controlled by a program which operates as a standard operation above the operating system. Underruns, therefore, occur primarily as a result of interruptions of the program; for example, interruption by a preemptive multi-tasking operating system. Thus, if a multi-task operating system such as Windows NT.TM., or OS2.TM. is used with the CPU, underruns can occur when the operating system takes control away from the program used to control data storage.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for a system and method of storing data to a recordable medium without interruption by an operating system.